Change the background color of specific block?

Question

I would like to start a different background color beginning from a function to the end.

Like this:

I'm aware you can define background colors from some faces like function and function names like foobar. But it affects only the background color of the words function and foobar. I would like to change the background color of the whole line where the function stats and end with it.

Why, you would ask? It would make it a lot easier for me to distinct which parts belongs to a funcion.

So I'm wondering if there is a pratical way to manage this in Emacs, of there is a Lisp package to achieve something like that?

Answer 1

1. You can use library Highlight to highlight a region using an overlay or text properties -- in particular, property face. To highlight the background, use a face that uses attribute background but not foreground.

   If you use text property face then you can also copy properties from some text and paste them to other text. So if your definition changes and becomes larger you can just copy some of the highlighted part and then paste its property face to the unhighlighted part.

   You could also use the functions defined in the library to do automatically (e.g. as a buffer-change hook or periodically, on a timer) extend the highlighting of a defun to accommodate changes to it.

   If you use an overlay then you can use the highlight-erasing commands (e.g., hlt-eraser) to remove only the last face you highlighted with. Drag the mouse over text where you want to remove the highlighting.

2. You could use ordinary font-locking. Add a pattern to font-lock-keywords that uses a function that recognizes the start and end of your definition. See the Elisp manual, node Customizing Keywords as well as the parent node, Font-Lock Mode and its other children.

---

UPDATE after your comment

I think maybe you are asking about highlighting not the region but the lines touched by the region, and extending highlighting past the end of text (including past any whitespace chars). Is that it? If so, try this:

(defun hlt-highlight-lines (start end face msgp)
  "Highlight full lines in region, window-wide."
  (interactive (list (save-excursion (goto-char (region-beginning))
                                     (line-beginning-position))
                     (save-excursion (goto-char (region-end))
                                     (line-beginning-position 2))
                     nil
                     t))
  (hlt-highlight-region start end face msgp))